Speeding black hole caught by Hubble

A black hole speeding through our Galaxy at about 400,000 kilometres per hour has been caught by the Hubble space telescope. The finding is great news for astronomers because it provides unique and compelling evidence that black holes really do form in supernova explosions, as theory predicts.

"The black hole must have been shot out of a supernova by the force of the explosion," says Roberto Mignani of the European Southern Observatory in Garching, Germany, one of the scientists who made the discovery.

Massive stars explode as supernovae at the end of their lives, leaving collapsed cores from which astronomers believe black holes can form. Theory says the gravity of black holes is so strong that nothing - not even light - can escape from their grip, so they are completely invisible. But astronomers have spotted about 10 possible black holes in the Milky Way because of their gravitational influence on nearby stars, dust and gas.

For instance, the Hubble telescope has seen one elderly star in the constellation Scorpius whirling round a dark object every two and a half days. Astronomers think the bright star, which lies about 6000 light years from Earth, is hostage to a black hole about five times as massive as the Sun.

On the run

Now a team led by Félix Mirabel of the French Atomic Energy Commission and the Institute for Astronomy and Space Physics of Argentina has used Hubble's sharp eyes to track the hostage star as the black hole drags it around.

They found that between 1996 and 2001, the pair moved about 70 millionths of a degree across the sky. This means they must be racing across the Galaxy at approximately 400,000 kilometres per hour - four times faster than the general drift of stars in their neighbourhood.

Only a violent birth in a supernova explosion could have made the black hole move so fast, the team concludes.

They hope to find more black holes on the run now that the European Space Agency has launched Integral, a gamma-ray satellite that will spy on hot material falling into these dark dungeons.

Journal reference: Astronomy and Astrophysics (vol 395, p 595)

If you would like to reuse any content from New Scientist, either in print or online, please contact the syndication department first for permission. New Scientist does not own rights to photos, but there are a variety of licensing options available for use of articles and graphics we own the copyright to.